1. Field of the Invention:
The present invention relates generally to a latch valve which is operated by a solenoid device and, more particularly, to an apparatus which incorporates a single permanent magnet and a magnetically sensitive device to indicate the position of a plunger that is actuated in response to a magnetic field provided by a solenoid.
2. Description of the Prior Art:
Many types of actuators are known to those skilled in the art. In certain types of actuators, solenoid apparatus is provided to cause a slidable plunger, or core, to move from a first position to a second position in response to a magnetic field induced by an electric current flowing through a coil of the solenoid. Many solenoid actuators of this type do not provide a means for determining the actual condition of the actuator. In other words, when an electric current is provided to the coil of the solenoid to move the plunger toward one position or the other, no means is readily available to determine if the plunger actually responded to the magnetic field. In solenoid actuators which are configured to provide a latching capability, wherein a momentary actuation of the solenoid causes the plunger to move into a first or a second position and other means are provided to hold the plunger in its position after the solenoid coil is deactivated, it is particularly important to be able to determine the actual position of the plunger. The means for determining the actual position of the plunger is important because several malfunctions can possibly cause the plunger to be in a position other than that which is intended. For example, the solenoid coil may not actually have been actuated by the anticipated flow of current through its conductor. This could be caused by a broken wire or a disconnection in the electrical circuit of the solenoid. Even if the solenoid operates properly and the plunger moves in the intended direction, a subsequent shock to the apparatus could possibly dislodge the plunger from its latched position.
In actuators which are provided with a latching capability, a solenoid coil is typically energized for a brief period of time to cause the core, or plunger, to move into contact with a stop member or plugnut. When the coil is de-energized, the plunger is maintained in the engaged position with the stop member by a permanent magnet which produces a continuous magnetic flux in the magnetic circuit in the same direction as that which was produced by the original energization of the coil. This causes the core to be latched in contact with the stop member by the permanent magnet flux. When the core, or plunger, is to be unlatched, the solenoid coil is energized with an electric current of opposite polarity to that current which was originally used to actuate the coil. Alternatively, a second coil can be wound in the solenoid in a direction which is opposite to the energizing coil. In both alternative applications, the coil produces a magnetic field which is opposite to the field produced by the permanent magnet and therefore allows a return spring to separate the plunger from the stop member and move the plunger to a position which is in noncontact association with the stop member. In these types of solenoid actuator apparatus, the solenoid coil is not continuously energized to maintain the core in either one of its two positions. Momentary electric pulses are applied to the coil, or coils, to cause the plunger to shift between its first and second positions.
As is known to those skilled in the art, certain devices have been developed to permit the detection of the position of the plunger relative to the stop member. One such device is described in U.S. Pat. No. 5,032,812, which issued to Banick et al on Jul. 16, 1991. The Banick et al patent discloses a solenoid actuator which has a magnetic flux sensor. The actuator comprises a coil or coils of electrical wire, a plugnut or stop member and a moveable core within the coils of the solenoid. A magnetic yoke surrounds the coil and the axis of the coil extends across the magnetic circuit defined by the yoke. Relatively large and small permanent magnets are associated with the yoke on opposite sides of the axis of the solenoid. The magnets produce flux in opposite directions to each other. A flux sensor, disposed closer to the small magnet than the large magnet, senses changes in direction of the flux. When the core and plugnut are separated, a large magnetic flux predominates throughout the yoke. When the core engages the plugnut, the small magnet flux predominates in its portion of the yoke. Changes in the direction of magnetic flux are detected by a sensor. Therefore, the sensor can be used to indicate the position of the core with respect to the plugnut.